The invention relates to hydrophilic microfibrillated articles; hydrophilic microfibers and microflakes; and methods of preparing each. The microfibrillated articles exhibit hydrophilic properties and wettability, and can be incorporated into or used as a large variety of useful products, such as water-absorbing wipes, mops, mats, tape backings, filters, fabrics, fabric replacements, and nearly any variety of other useful industrial and commercial products where hydrophilicity is desired.
Materials that can be processed to form microfiber-bearing surfaces have been identified, including oriented polypropylene. See, e.g., U.S. Pat. No. 6,110,588. Microfibrillatable materials of U.S. Pat. No. 6,110,588 can be prepared from certain materials and processed using various techniques to produce oriented films capable of being microfibrillated. Microfibrillation of these oriented films results in, e.g., a microfiber-bearing surface, the microfiber being a specific size and shape.
Fibrillated (e.g., microfibrillated) surfaces and articles exhibit a variety of uses, by themselves or in combination with other materials that may or may not include a fibrillated surface. For example, certain fibrillated articles can be used as a wipe, a wrap, a backing, a fabric, a filter, etc. In some of these applications, it can be desirable to select a fibrillated surface that exhibits a physical or chemical property suited for a particular application. For instance, it can be useful in certain applications to select a fibrillated surface that includes any one or more of hydrophilic, hydrophobic, oleophilic, oleophobic, inert or stain resistant, electrostatically chargeable material, etc.
Certain melt-processable polymers that can be used to prepare microfibrillatable and microfibrillated materials are not especially hydrophilic. Polyolefins such as polypropylene, for example, and other similar polymeric materials useful in forming microfibrillated surfaces, are generally not hydrophilic due to their non-polar nature. Thus, it would be desirable to identify methods or materials that could be used to improve the hydrophilicity of such melt-processable polymers useful in forming microfibrillated surfaces. It can be unpredictable, however, whether or not the chemistry of melt-processable materials and hydrophilic materials will allow the hydrophilic material to be incorporated into and retained within a melt-processable polymer, through processing of the melt-processable polymer en route to a microfibrillated surface. As a single example, certain water-soluble hydrophilic surfactants or hydrophilic polymers may be expected to be washed away or dissolved during hydroentanglement or other microfibrillation processes, and therefore may not be expected to remain with a microfibrillated article to improve hydrophilicity.
Furthermore, in preparing a microfibrillated article, selection of ingredients can be important to succeed in producing a fibrillated surface. A typical method of preparing a microfibrillated article includes: selecting a polymer that is capable of being melt-processed to form a fibrillated surface such as a film; melt-processing the film so that the film is capable of being fibrillated, such as by stretching, orienting, lengthening, etc.; and microfibrillating, e.g., hydroentangling, the film to disrupt the surface of the film in a manner to form a microfibrillated surface. Each of the steps must be performed, and the materials of the film must be selected, with the design of providing an extruded, oriented film that has a morphology and mechanical and chemical makeup to allow the film to be processed to a microfibrillated surface.
While various additives might be thought to be generally useful if added to a melt-processable or microfibrillatable polymer useful to prepare a microfibrillated article, a balance of morphology, e.g., crystallinity, and other properties such as the presence and concentration of voids, molecular orientation, polymeric strength, etc., is required to extract a microfibrillated surface from a melt-processable polymeric material. Any additive material included in a polymer or polymeric film being processed to form a microfibrillated article has the potential to detrimentally affect the ability of the film material to be processed to a microfibrillated surface. For example, an additive may frustrate the ability of a polymer to be melt-processed (e.g., extruded), calendered and/or length oriented, or microfibrillated. The additive may, for example, prevent a useful mixture from being formed by melt-processing; weaken the composition of a melt-processed polymeric material, preventing processing such as orientation, stretching, or calendering, etc.; or may allow melt-processing and orienting, but may have the effect of frustrating microfibrillation, e.g., by not allowing the formation of voids, or by otherwise disturbing the morphology, crystallinity, or other physical features necessary in a film to allow microfibrillation.
New and different microfibrillated articles and methods for their preparation are always desirable. In particular, there continues to be a need for microfibrillated articles that exhibit improved properties such as improved wettability or hydrophilicity.
The invention relates to hydrophilic microfibrillated microflake or microfiber articles and their preparation. The microflakes or microfibers can be prepared by including a hydrophilic component with a melt-processable polymer, in appropriate amounts, so that the melt-processable mixture of melt-processable polymer and hydrophilic material may be processed to be microfibrillated to form microflakes or microfibers.
According to the invention, a hydrophilic component can be included in a melt-processable polymer in an amount that will improve the hydrophilicity of the material, but will at the same time not prevent the material from being melt-processed to form a film, followed by other necessary processing to form a microfibrillated microfiber or microflake surface.
The invention can be accomplished using any of a variety of melt-processable polymers capable of being processed to form microflakes or microfibers. Certain important examples include polyolefins such as polyethylene, polypropylene, polyester, and their mixtures, but many others as well, with or without additional ingredients such as a void initiating agent or blowing agent.
The invention can be accomplished using any of a variety of hydrophilic components combined with the melt-processable polymer in an amount that will still allow a variety of processing steps that result in a microfibrillated surface. Important examples include certain hydrophilic polymers and certain hydrophilic surfactants, particularly nonionic hydrophilic surfactants.
As used herein, xe2x80x9chydrophilic,xe2x80x9d xe2x80x9chydrophilicity,xe2x80x9d and similar terms are used to describe materials that can be wet by water, by aqueous solutions of acids and bases (e.g., aqueous potassium hydroxide), by polar liquids (e.g. sulfuric acid and ethylene glycol), or combinations thereof. (See, U.S. Pat. No. 5,804,625). In certain preferred embodiments of the invention, microfibrillated microflake or microfiber articles can be sufficiently hydrophilic to about 5 or 10 grams of water per gram of microfibrillated article. Other embodiments of microfibrillated articles of the invention can be sufficiently hydrophilic to have the ability to increase the amount of absorbed water at least 30% and up to 1000% or more, e.g., 200%, compared with the same article without the hydrophilic component.
Thus, an aspect of the invention relates to a hydrophilic microfibrillated article that includes an oriented melt-processed polymeric material, wherein the polymeric material includes a melt-processed polymer that is a polypropylene, a polyethylene, or a mixture thereof, and hydrophilic component preferably in an amount effective to improve the hydrophilicity of the microfibrillated article.
Another aspect of the invention relates to a hydrophilic article that includes an oriented melt-processed polymeric material, and the polymeric material contains high melt strength polypropylene and hydrophilic component.
Yet another aspect of the invention relates to a hydrophilic microfibrillated article containing oriented melt-processed polymeric material, wherein the polymeric material includes melt-processed polymer and hydrophilic surfactant.
Yet another aspect of the invention relates to a hydrophilic microfibrillated article including oriented melt-processed polymeric material, wherein the polymeric material contains melt-processed polymer and hydrophilic polymer, and the hydrophilic polymer is selected from a sulfonated polyester and a polyvinylpyrrolidone.
Yet another aspect of the invention relates to a method of preparing a hydrophilic microfibrillated article. The method includes extruding a mixture of melt-processable polymer and hydrophilic component to form a film, orienting the film to form a microfibrillatable material, and microfibrillating the microfibrillatable material to form a hydrophilic microfibrillated article.
The invention relates to preparing microfibrillated articles that include hydrophilic microfibrillated microflakes or microfibers. The microfibrillated articles are generally prepared from a melt-processable combination of ingredients that include a melt-processable polymer and a hydrophilic component. The hydrophilic component may or may not be melt-processable on its own.
The microfibrillated articles are prepared from selected materials, typically in the form of a melt-processed polymer converted to a polymeric film that can be microfibrillated to form a fragmented piece of the film in the form of a microfiber or microflake. Such microfiber or microflake-forming materials are referred to herein as xe2x80x9cmicrofibrillatable materials.xe2x80x9d
As used herein, the terms xe2x80x9cmicroflake or microfiber articlexe2x80x9d and xe2x80x9cmicrofibrillated articlexe2x80x9d refer to microfibrillated materials that have a surface structure that includes a microfiber or a microflake, or a similarly-sized and shaped surface structure created by microfibrillation. One type of such structure, a microfiber, is understood to have size and shape characteristics including an effective diameter less than 20 microns and a transverse aspect ratio from 1.5:1 to 20:1, a cross-sectional area of about 0.5xcexc2 to about 3.0xcexc2, and can provides a preferred surface with a surface area of 0.5 to 30 square meters per gram. Another type of microfibrillated structure, a microfibrillated microflake or xe2x80x9cmicroflake,xe2x80x9d is understood to comprise a schistose structure. In this structure, the microflakes, which tend to be generally parallel to one another, are shaped like a plate or a plate-like ribbon where the length scale of two of the microflake dimensions is at least 10 times, preferably at least 20 times, the length scale of the microflake""s third dimension. The microflakes typically can have an average length or thickness of less than 20 micrometers, preferably less than about 5 micrometers, more preferably about 1 to about 3 micrometers. The microflakes can have an average width of less than about 200 micrometers, preferably less than about 80 micrometers, more preferably about 5 to about 30 microns. The aspect ratio of the surface of microflakes may range from, e.g., 1:1 to 1:20, and can depend on how balanced the orientation is. A more unbalanced stretch leads to a more tape-like microflake. The flakes can be connected to one another and tend to be continuous in a width or length direction. Dimensions can be measured using a scanning electron microscope.
Examples of microflake and microfiber structures are described in Assignee""s copending patent applications U.S. Ser. No. 09/602,978, xe2x80x9cFibrillated Article and Method of Making,xe2x80x9d filed on Jun. 23, 2000; U.S. Ser. No. 09/858,253, filed on May 15, 2001, entitled xe2x80x9cFiber Films and Articles from Microlayer Substratesxe2x80x9d; and also in U.S. Pat. Nos. 6,110,588, and 6,333,433 all of which are incorporated herein by reference.
The terms microflake and microfiber do not include electret fiber materials as described in a U.S. Pat. No. Re. 30,782, which are prepared by mechanical fibrillation through the entire thickness of an oriented film to form fibers. Characterization of one example of fibers prepared according to Re. No. 30,782 revealed fiber dimensions of 10 micrometers thick by 40 micrometers wide, with an effective diameter of 25 micrometers.
Microfibrillatable materials include a variety of melt-processable or polymers or melt-processed polymeric films that can be further processed by microfibrillation to form microfibers or microflakes. In general, microfibrillatable materials that can be microfibrillated to form microfibers or microflakes include materials capable of being processed by mechanical or other action, especially by microfibrillation with a fluid, to cause a breaking, splitting, or other form of fragmenting or disruption of the material to form a microfiber or microflake on or from a surface of the material. Important representative examples of microfibrillatable materials include extruded, oriented, polymeric film materials having proper morphology to allow microfibrillation to a microflake or microfiber, especially by hydroentangling techniques.
Microfibrillatable materials are typically made of melt-processed polymeric materials having a structure or morphology that includes at least one feature that upon mechanical contact will cause a microflake or microfiber to be formed from the polymeric film, typically including proper orientation of the polymeric material. Properties of a film that facilitate formation of flakes or microfibers can include: structural features such as voids, microvoids, or other disturbances in the polymer; orientation of the film, e.g., biaxial or uniaxial orientation; multiple layers, especially where an interface at surfaces of different layers weakens the internal structure of a multi-layer film, or where the films are extremely thin such as xe2x80x9cmicrolayer filmsxe2x80x9d; and morphology, such as crystallinity. Proper orientation can be present alone in a film to allow microfibrillation. Alternatively, orientation and one or more other of these different features can be present in combination. When combinations of different properties are present, the amount or severity of one or both properties may be reduced relative to the amount or severity of that property that would be necessary to allow fibrillation if only that single property were present.
Polymers useful in preparing hydrophilic microflakes or microfibers of the invention include a variety of different melt-processable polymeric materials and mixtures and blends of different polymeric materials. An important example of a useful class of melt-processable polymers is polyolefins, including polyethylenes and polypropylenes, specifically including isotactic polypropylene, syndiotactic polypropylene, mixtures of isotactic, atactic and/or syndiotactic polypropylene, and mixtures of any one of these with another melt-processable polymer.
Properties that may facilitate microfibrillation can be created in a film during processing of the film. In general, the described properties and combinations of the properties can be produced in a polymeric film by selecting one or more of the following: composition of the polymeric material; processing conditions, e.g., processing conditions during extrusion or co-extrusion of a melt-processable polymeric mixture; multiple layers of a film, e.g., a microlayer film; processing conditions after extrusion or co-extrusion, possibly including individual steps or combinations of steps such as casting, quenching, annealing, calendering, orienting, solid-state drawing, roll-trusion, and the like.
Polymeric films typically comprise long molecular chains having a backbone of carbon atoms. The ability to microfibrillate a surface of a polymeric film is often not realized due to random orientation and entanglement of the individual polymer chains. As one method of facilitating microfibrillation, polymer chains can be oriented to be relatively more parallel to one another and partially disentangled. The degree of molecular orientation can be defined in terms of a draw ratio, which is the ratio of a final length to an original length. Orientation may be effected by a combination of techniques, including the steps of calendering and length orienting.
Microfibrillation of polymeric films can be facilitated by orientation of the film, including either bi-axial or uni-axial orientation. Bi-axial orientation means that a film is substantially lengthened or stretched in two directions. Uni-axial orientation means that a film is lengthened or stretched in one direction relatively more than it is stretched in another, e.g., perpendicular direction. By exemplary methods, a film can be stretched in a machine direction while its width is not held, and the film gets longer in length, thinner, and narrower in width. In another exemplary method, the width may be held constant while the length is stretched. In other words, sufficient orientation may be achieved for microfibrillation by inducing a relatively greater amount of orientation in one direction, e.g., the machine direction, compared to a lesser degree of orientation in another direction, especially a perpendicular direction, such as the cross direction.
Crystallinity also can affect the ability of a film, particularly a uniaxially oriented film, to be microfibrillatable. A variety of semi-crystalline, crystalline, and highly-crystalline materials can be processed to be microfibrillatable and able to be processed to form microfibers or microflakes. Examples of polymeric materials for forming microfibrillatable films can include semicrystalline melt-processed films having a maximized crystallinity induced in the polymeric film layer by an optimal combination of casting and subsequent processing such as calendering, annealing, stretching, and recrystallizing. For polypropylene, as an example, preferred crystallinity can be above 60%, preferably above 70%, most preferably above 75%. The crystallinity may be measured by differential scanning calorimetry (DSC) and comparison with extrapolated values for 100% crystalline polymers. See, e.g., B. Wunderlich, Thermal Analysis, Academic Press, Boston, Mass., 1990.
Microflake and microfiber-forming microfibrillatable materials and films also may contain spherulites and microvoids to facilitate fibrillation. See, e.g., U.S. Pat. No. 6,110,588.
Any suitable combination of polymer film composition and processing steps and conditions may be used to impart sufficient orientation and microscopic structure, e.g., crystallinity, voids or microvoids, spherulites, multiple layers, microlayers, etc., to produce a microfibrillatable material such as a film or layer of a multi-layer film that can be microfibrillated to form microflakes or microfibers. These conditions may include combinations of casting, quenching, annealing, calendering, orienting, solid-state drawing, roll-trusion, and the like.
Some specific examples of melt-processable materials that can be used to prepare a microfibrillatable material layer are discussed in U.S. Pat. No. 6,110,588. Exemplary semicrystalline polymers include high and low density polyethylene, polyoxymethylene, polypropylene, poly(vinylidine fluoride), poly(methyl pentene), poly(ethylene-chlorotrifluoroethylene), poly(vinyl fluoride), poly(ethylene terephthalate), poly(butylene terephthalate), nylon 6, nylon 66, polybutene, and thermotropic liquid crystal polymers, blends of any one or more of these polymers with another of these or another polymer or a copolymer made from any of the listed monomers and any other listed monomer or a different monomer. Important examples of useful polymers include polyolefins such as polypropylene and polyethylene which are readily available at low cost and can provide highly desirable properties in microfibrillated articles such as high modulus and high tensile strength.
The molecular weight of the polymer can be chosen so that the polymer is melt-processable (i.e., extrudable or co-extrudable) under the processing conditions used in extrusion and co-extrusion, and in combination with a useful amount of the hydrophilic component. For polypropylene and polyethylene, for example, the molecular weight may be from about 5,000 to 499,000 and is preferably from about 100,000 to 300,000.
Still referring to the ""588 patent, it describes that any suitable combination of processing conditions may be used to impart crystallinity and orientation to a melt-processed film. Starting with a melt-processed, cast film, for example, the film may be calendered, stretched, oriented, cast, quenched, annealed, drawn, roll-truded, etc. Such processing generally serves to increase the degree of crystallinity of the polymer film as well as the size and number of spherulites.
The ""588 patent describes additional details and recites examples of preferred embodiments of materials and techniques, and optional processing steps, that may be used to prepare useful microfibrillatable materials. That description along with the present disclosure and knowledge available to a skilled artisan will enable the preparation of films and articles described herein.
Another class of microfibrillatable materials that can be used according to the invention includes foamed and oriented polymers, preferably thermoplastic polymers. The foam may be made using extrusion processing, for example, by adding one or more polymers and gas or supercritical fluid (SCF) to a twin-screw (TSE) or single-screw extruder (SSE). One way to add gas to the polymer stream is to use a chemical blowing agent (CBA) such as azodicarbonamide or a sodium bicarbonate/citric acid blend. The CBA degrades at elevated temperatures, generating gas either through decomposition or reaction. Another way to add gas to the polymer stream is to use a physical blowing agent (PBA) such as carbon dioxide, nitrogen, or pentane. The gas or SCF and polymer are thoroughly mixed, preferably into a one-phase mixture, at elevated pressure. When the resulting mixture exits the extruder, the polymer is foamed, and the resulting extruded foam typically has a density that is about twenty to eighty percent less than the neat unfoamed polymer.
The foamed polymer is then uniaxially or biaxially oriented. To uniaxially orient the foamed polymer, the foam is fed into a length orienter (LO) and oriented to between about 2 and 12 times the original length. To orient foams in a biaxial manner, an LO combined with a tenter may be used to sequentially orient the foam in the machine and transverse directions. Similarly, simultaneous biaxial orientation equipment, such as a tenter with accelerating clips, can be used to generate more isotropic oriented foams. The orientation process can raise or lower the density of the foam, depending on process conditions. However, the oriented foam typically has a density of about twenty to eighty percent less than the neat unfoamed polymer. Generally, lower density foams have higher void content, which increases the rate of microfibrillation.
While oriented foams can be generated in a variety of processes, preferably the foams can be made in a manner similar to that described in Assignee""s copending patent application U.S. Ser. No. 09/602,032, xe2x80x9cFoam and Method of Making,xe2x80x9d filed on Jun. 21, 2001, and incorporated herein by reference. The foams created using the process and materials described therein feature much smaller cell sizes than conventional foams, thus providing a more visually appealing, more uniform, and more microfibrillatable material.
See also Assignee""s copending patent application U.S. Ser. No. 09/602,978, xe2x80x9cFibrillated Article and Method of Making,xe2x80x9d filed on Jun. 23, 2000, incorporated herein by reference, disclosing fibrillated materials made from foamed and oriented high melt strength polypropylenes, which are useful polymers for making foams according to the present invention. High melt strength polypropylenes are considered to include polypropylenes having melt strengths in the range of 25 to 60 cN at 190xc2x0 C. Melt strength may be measured using an extensional rheometer by extruding the polymer through a 2.1 mm diameter capillary having a length of 41.9 mm at 190xc2x0 C. and at a rate of 0.030 cc/sec; the strand is then stretched at a constant rate while measuring the force. Preferably the melt strength of a high melt strength polypropylene can be in the range of 30 to 55 cN, as described in WO 99/61520, the entirety of that disclosure being incorporated herein by reference. Examples of typical high melt strength polypropylenes include branched polypropylenes. The polypropylenes may be homopolymers or copolymers, with co-monomers including ethylene.
Exemplary high melt strength foamable polypropylenes may consist of propylene homopolymers or may comprise a copolymer having 50 wt % or more propylene monomer content. The foamable polypropylene may comprise a mixture or blend of propylene homopolymers or copolymers with a homo- or copolymer other than propylene homo- or copolymers.
Particularly useful high melt strength propylene copolymers are those of propylene and one or more non-propylenic monomers. Propylene copolymers include random, block, and graft copolymers of propylene and olefin monomers selected from the group consisting of C3-C8 xcex1-olefins and C4-C10 dienes. Propylene copolymers may also include terpolymers of propylene and xcex1-olefins selected from the group consisting of C3-C8 xcex1-olefins, wherein the xcex1-olefin content of such terpolymers is preferably less the 45 wt %. The C3-C8 xcex1-olefins include 1-butene, isobutylene, 1-pentene, 3-menthyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexane, and the like. Examples of C4-C10 dienes include 1,3-butadiene, 1,4-pentadiene, isoprene, 1,5-hexadiene, 2,3-dimethyl hexadiene and the like.
Other polymers that may be added to the high melt strength polypropylene in the foamable composition including high, medium, low and linear low density polyethylene, fluoropolymers, poly (1-butene), ethylene/acrylic acid copolymer, ethylene/vinyl acetate copolymer, ethylene/propylene copolymer, styrene/butadiene copolymer, ethylene/styrene copolymer, ethylene/ethyl acrylate copolymer, ionomers and thermoplastic elastomers such as styrene/ethylene/butylenes/styrene (SEBS), and ethylene/propylene/diene copolymer (EPDM).
As described above, a variety of blowing agents may be used. The amount of blowing agent incorporated into a foamable polymer mixture can be chosen to yield a foam having a void content in excess of 10%, and even in excess of 20%, as measured by density reduction; i.e., 1xe2x80x94(the ratio of the density of the foam to that of the neat polymer)xc3x97100. Generally, these greater foam void contents can enhance fibrillation and can produce a greater yield of a fibrillated surface.
Another type of microfibrillatable material that can be used according to the invention to produce hydrophilic microflakes or microfibers and microfibrillated articles are those polymeric oriented film materials described in Applicants"" U.S. Pat. No. 6,331,433, entitled xe2x80x9cFilms Having a Fibrillated Surface and Methods of Making.xe2x80x9d
According to that description, oriented, immiscible mixtures of semicrystalline polymer and void-initiating component are prepared such that they can be microfibrillated. The films can be produced by providing an oriented polymeric film comprising an immiscible mixture of a crystalline polymer and a void-initiating component, stretching the film along at least one major axis to impart a voided morphology, optionally stretching the film along a second major axis, and microfibrillating the voided film, e.g., with fluid energy, to produce microfibers or microflakes.
The term xe2x80x9cvoid-initiating componentxe2x80x9d refers to ingredients that have the effect of producing voids that facilitate microfibrillation, and includes the foaming agents mentioned above. The void-initiating component can also be a polymeric material or a solid material, such as a material that is immiscible in the melt-processable polymer, as just mentioned.
Important examples of void-initiating agents include organic and inorganic solids having an average particle size of from about 0.1 to 10.0 microns and may be any shape including amorphous shapes, needles, spindles, plates, diamonds, cubes, and spheres. Useful inorganic solid void initiating components include solid or hollow glass, ceramic or metal particles, microspheres or beads; zeolite particles; inorganic compounds including but not limited to metal oxides such as titanium oxide, alumina, and silicon dioxide; metal, alkali- or alkaline earth carbonates or sulfates; kaolin, talc, carbon black, silicates including calcium metasilicates (e.g., wollastonites), and the like. Inorganic void initiating components can be chosen to have little surface interaction, due to either chemical nature or physical shape, when dispersed in a semicrystalline polymer component. In general, preferred inorganic void initiating components should not be chemically reactive with the semicrystalline polymer component, including Lewis acid/base interactions, and preferably have minimal van der Waals interactions.
Certain preferred void initiating agents can include thermoplastic polymers, such as semicrystalline polymers and amorphous polymers, to provide a blend immiscible with the semicrystalline polymer component. An immiscible blend shows multiple amorphous phases as determined, for example, by the presence of multiple amorphous glass transition temperatures.
Polymers useful as void initiating component include semicrystalline polymers described herein, as well as amorphous polymers, selected to form discrete phases upon cooling from a melt. Useful amorphous polymers include polystyrene, polymethylmethacrylate, polycarbonate, cyclic olefin copolymers (COCs) such as ethylene norbornene copolymers, and toughening polymers such as styrene/butadiene rubber (SBR) and ethylene/propylene/diene rubber (EPDM). Specific useful combinations of immiscible polymer blends include, for example, polypropylene and polybutylene terphthalate, polypropylene and polyethylene terphthalate, polypropylene and polystyrene, polypropylene and high density polyethylene, polypropylene and low density polyethylene, polypropylene and polycarbonate, polypropylene and polymethylpentene; and polypropylene and nylon.
Preferred amounts of such void initiating components included in a fibrillatable material can be in from 1 to about 49 percent by weight, e.g., from 5 to about 40 percent by weight, or from about 10 to about 25 percent by weight, so that the first semicrystalline polymer forms a continuous phase and the void initiating component forms a discrete, discontinuous phase.
Other details and preferred aspects of microfibrillatable polymeric materials are described in the Assignee""s U.S. Pat. No. 6,331,433. Such information, in combination with the present description, will be useful for the skilled artisan to prepare hydrophilic microflakes and microfibers and microfibrillated articles containing a hydrophilic component, according to the invention.
Another type of fibrillatable material that can be used according to the invention to produce hydrophilic microfibers and microflakes, and microfibrillated articles, includes those polymeric multi-layer films sometimes referred to as xe2x80x9cmicrolayer films.xe2x80x9d Microlayer films are known in the arts of polymeric films, and are well known for their optical properties. Examples of microlayer film constructions and methods for preparing microlayer films (and some explanation of their uses and principles of their operation) are described, for example, in the following United States patents: U.S. Pat. Nos. 5,269,995, 6,124,971, and 6,101,032. Assignee""s copending United States patent application entitled xe2x80x9cFiber Films and Articles from Microlayer Substrates,xe2x80x9d filed May 15, 2001, and assigned U.S. Ser. No. 09/858,253, the disclosure of which is incorporated herein by reference.
Microlayer films are generally understood, and are known for their specialty optical properties. Microlayer films useful according to the invention, while being similar in construction and methods of preparation, are prepared with the idea of forming microflakes or microfibers from the film, as opposed to providing films with select optical properties.
Microlayer films can be produced from a great variety of polymeric materials co-extruded to form a stack of multiple (preferably a large number) layers of one or different polymers, copolymers, or mixtures of polymers, having very small, preferably extremely small thicknesses.
The thickness of the total film and the individual layers of a microlayer film can be any thicknesses that will allow microfibrillation. Each of these thickness values may have practical limitations based on processing considerations, such as the total maximum number of layers that can be cast using a co-extrusion process, the minimum thickness of such layers, and the total thickness of a coextruded film that can be either cast or further processed, e.g., calendered.
A microlayer film can include tens, hundreds, thousands, or tens of thousands of layers of the same, similar, or any number of different polymeric compositions, which may be a single polymer, a copolymer, or a mixture of two or more polymers or copolymers. Reasons for choosing a polymer or copolymer as part of a stack can depend on various factors relating especially to the desired properties of different layers of the stack; how those properties relate to other layers of a stack; and the ability of different types of materials to form microflakes or microfibers; among other factors. For instance, microlayers of two or many more polymeric materials can be included in a single microlayer stack to obtain a microlayer film that can be microfibrillated to produce microflakes or microfibers with any number of different polymers and properties on a single microfibrillated surface.
The microlayer film can contain as many materials as there are layers in the stack, or more. For ease of manufacture, preferred stacks may contain only a few different materials, or only one or two.
Examples of useful polymer materials for layers of a microlayer film can include such polymeric materials as polyethylene naphthalate (PEN); polyesters such as polyethylene terephthalate (PET); amorphous copolyesters, copolymers of PEN such as 90/10 Co-PEN; PETG glassy PET); poly methyl(meth)acrylate and copolymers thereof; polypropylene; polystyrene; atactic polystyrene; polyethylene; fully saturated ethylene/propylene rubber in a polypropylene matrix; metallocene poly(alpha-olefin); ethylene-propylene; ethylene vinyl acetate in polypropylene; maleate grafted polypropylene in polypropylene, and the like.
Certain microlayer films can be oriented, especially uni-axially oriented, to cause one or more of the layers to become a microfibrillatable layer.
Microlayer films can be produced using co-extrusion techniques and equipment generally known to the skilled artisan. Generally, according to co-extrusion methods, multiple streams of one or a number of different melt-processable polymeric materials are divided to flow through a modular feedblock, which may be further divided into substreams and re-combined into a composite stream that passes through an extrusion die to form a multi-layer film in which each very thin layer is generally parallel to the major surfaces of adjacent layers.
The number of layers in the film can be selected to achieve desired fibrillation properties, typically using a minimum number of layers for reasons of film thickness, flexibility and economy. While films having more layers can also be useful, e.g., up to 40,000 layers or more, useful films can typically have fewer than 10,000 layers, more preferably fewer than 5,000, and even more preferably fewer than 2,000 or 1,000 layers.
Typical total thicknesses of cast (in-process microlayer) films, after extrusion but prior to any post-extrusion processing such as lengthening or calendering, can be in the range from about 5 mils (127 xcexcm) to about 400 mils (10,160 xcexcm), e.g., from about 10 mils (254 xcexcm) to about 400 mils (10,160 xcexcm), e.g., 10 to 100 mils (254 xcexcm to 2540 xcexcm), and with the range from about 30 mils (762 xcexcm) to about 65 mils (1651 xcexcm) sometimes being preferred. The thickness of typical layers of a microlayer film, as extruded and prior to subsequent processing such as calendering and stretching, can be any thickness, generally from about 2 microns to about 10,000 microns, with typical thicknesses being approximately in the range from about 2 microns to about 100 microns.
The ability to achieve microfibrillation of a microlayer film can be influenced by the composition of the layers, the number of layers and thickness of each layer, and processing conditions used to prepare the film. In the case of organic polymers that can be oriented by stretching, the films are generally prepared by extruding and orienting by stretching at a selected temperature, optionally followed by heat-setting at a selected temperature. Alternatively, the extrusion and orientation steps may be performed simultaneously. It has been found that microfibrillation of a microlayer film can be achieved by stretching a film substantially in one direction (uniaxial orientation or mono-axial). A uni-axial orientation of 3:1 or more is typically useful, for forming microfibers.
Methods for producing any of various types of microfibrillatable materials and films are well known in the arts of polymeric materials and film processing. Melt-processable polymers and other materials can be used with those methods, and with a hydrophilic component according to the invention, based on proper selection of the chemistries, properties, and amounts of each, to produce microfibrillatable materials or films for production of hydrophilic microfibers and microflakes. Examples of useful techniques include extrusion, co-extrusion, lamination, and other known methods of processing films, all of which are well known and understood in the polymer film arts. Useful equipment for producing the films will also be apparent to those of ordinary skill, including extruders, multi-cavity die extruders, and laminators, as well as various other types of equipment known in the arts of films and film processing, some of them being mentioned herein. Also well known are subsequent processing techniques for films such as casting, quenching, annealing, calendering, orienting, solid-state drawing, roll-trusion and the like. Using these techniques, suitable equipment, and the present disclosure, a skilled artisan will be able to prepare microfibrillatable materials and microfibrillated articles according to the invention.
Generally, according to the invention, a hydrophilic component can be included in a melt-processable polymeric material, e.g., as described above, to be processed together to a microfibrillated article. According to the invention, the chemistry and amount of hydrophilic component can be selected so that the melt-processable material containing melt-processable polymer and hydrophilic component can still be processed to a microfibrillated microflake or microfiber surface, meaning that the mixture of melt-processable polymer and hydrophilic component remains melt-processable to form a film that can be further processed to a microfibrillatable film (e.g., by extension, orienting, or calendering, etc.), and that the melt-processed and further processed film can be microfibrillated to form hydrophilic microflakes or microfibers at a surface of the film.
Whether or not an amount of a particular hydrophilic component can successfully be included in a melt-processable polymer and processed to produce hydrophilic microflakes or microfibers as discussed above can be determined starting from the present description generally, and more specifically as follows. As one criterion, a hydrophilic component should be able to be uniformly mixed, blended, dissolved, or otherwise incorporated into a melt-processable polymer in an amount that will produce hydrophilicity in a resulting microfibrillated microflake or microfiber, but that will not eliminate the melt-processable nature of the mixture of melt-processable polymer and hydrophilic component. In other words, a hydrophilic component should be capable of being added to melt-processable polymer, and the mixture should be capable of being melt-processed into a film having useful mechanical properties and good consistency and uniformity, at least sufficient to process the extruded film further toward a microfibrillated article. Also, a hydrophilic component can be selected and added in an amount that will allow the film of the melt-processed polymer and hydrophilic component mixture to be extended, length oriented, or calendered, to provide the film with a proper combination of mechanical properties, chemical properties, physical properties (e.g., voids), and morphological properties (e.g., crystallinity and orientation), to form microflakes or microfibers upon microfibrillation; and the film should be capable of being stretched, oriented, or otherwise processed, without breaking or tearing, to provide an oriented film capable of being microfibrillated to form microflakes or microfibers. A hydrophilic component should also be selected so the melt-processed and oriented film of polymer and hydrophilic component mixture can be processed to form hydrophilic microfibers or microflakes from the film by microfibrillation, e.g., the processed film maintains sufficient mechanical properties to withstand microfibrillation, and, based on the morphology, etc., as just mentioned, can form microfibers and/or microflakes when microfibrillated. Finally, the hydrophilic component must still be present and effective in the microfibrillated structure to improve hydrophilicity of the polymeric material. Not all of the large number of known and commercially available hydrophilic materials will be useful according to these criteria, with any one or more melt-processable polymer useful to form a microfibrillatable film. A skilled artisan, based on the present disclosure, will be sufficiently informed to identify hydrophilic components that can be used to form hydrophilic microflakes and microfibers, as well as their useful amounts, in combination with different types of melt-processable polymers, such as those containing void initiating components, those containing microlayers, and those processed to include a blowing agent, as well as others.
A type of useful hydrophilic component is the class of materials known as hydrophilic surfactants. Hydrophilic surfactants include well known commercially available materials, and come in a variety of different chemistries, including anionic, nonionic, cationic, and amphoteric chemistries, etc., as well as many varieties of different chemical compound species within each of these broader classes, e.g., fluorinated, non-fluorinated, and those substituted with chemical functional groups such as acidic groups (e.g., carboxylic acids), amides, amines, hydroxyls, and others.
Useful fluorochemical surfactants include fluoroaliphatic group-containing nonionic compounds that contain one or more blocks of water-solubilizing polyoxyalkylene groups in their structures. A class of such surfactants is described in U.S. Pat. No. 5,300,357 (Gardiner), the description of which is incorporated herein by reference. Generally, a type of fluorochemical surfactant useful in the invention includes those represented below by Formula I:
(Rf-Q)n-Zxe2x80x83xe2x80x83(I) 
wherein:
Rf is a fluoroaliphatic group having at least 4 fully-fluorinated carbon atoms that may be straight-chained, branched, or, if sufficiently large, cyclic, or any combination thereof. The skeletal chain in the fluoroaliphatic radical can include one or more caternary heteroatoms, such as oxygen, hexavalent sulfur, and trivalent nitrogen atoms, bonded only to carbon atoms of the skeletal chain. Fully fluorinated fluoroaliphatic groups are preferred, but hydrogen or chlorine atoms may be present as substituents, provided that not more than one atom of either is present for every two carbon atoms. While Rf can contain a large number of carbon atoms, compounds where Rf is not more than 20 carbon atoms may typically be adequate, because longer Rf chains usually represent a less efficient use of the fluorine than is possible with shorter chains. Fluoroaliphatic groups or chains containing from about 4 to about 12 carbon atoms can be preferred. Generally, Rf can contain between about 40 and about 78 weight percent fluorine. The terminal portion of the Rf group can preferably contains at least four fully fluorinated carbon atoms, e.g., CF3CF2CF2CF2xe2x80x94, and particularly preferred compounds are those in which the Rf group is fully or substantially completely fluorinated, as in the case where Rf is a perfluoroalkyl, e.g., CF3(CF2)nxe2x80x94. Suitable Rf groups include, for example, C4F9xe2x80x94, C8F17xe2x80x94, C6F13CH2CH2xe2x80x94, and C10F21xe2x80x94CH2CH2xe2x80x94.
Q in Formula I above is a multivalent, generally divalent, linking group, or is a covalent bond, that provides a means to link Rf with the depicted group Z, Q can comprise a heteroatom-containing group, e.g., a group such as xe2x80x94Sxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94N(R)xe2x80x94 (where R is a hydrogen or a C1 to C6 substituted or unsubstituted alkyl group that may comprise a catenary heteroatom such as O, N, S), xe2x80x94CnH2nxe2x80x94 (n=1 to 6); Q can comprise a combination of such groups, such as would give, for example,
xe2x80x94CON(R)CnH2nxe2x80x94, xe2x80x94SO2N(R)CnH2nxe2x80x94, xe2x80x94SO3C6H4N(R)CnH2nxe2x80x94,
xe2x80x94SO2N(R)CnH2nO[CH2CH(CH2Cl)O]gCH2CH(CH2Cl)xe2x80x94 (n=1 to 6; g=1 to 10),
xe2x80x94SO2N(CH3)C2H4OCH2CH(OH)CH2xe2x80x94, xe2x80x94SO2N(C2H5)C2H4OCH2CH(OH)CH2xe2x80x94,
xe2x80x94SO2N(H)CH2CH(OH)CH2NHC(CH3)CH2xe2x80x94, xe2x80x94(CH2)2S(CH2)2xe2x80x94, and
xe2x80x94(CH2)4SCH(CH3)CH2xe2x80x94.
Z in Formula I above is a nonionic, water-solubilizing group comprising a poly(oxyalkylene) group, (ORxe2x80x2)x, where Rxe2x80x2 is an alkylene group having from 2 to about 4 carbon atoms, such as xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2CH2xe2x80x94, xe2x80x94CH(CH3)CH2xe2x80x94, and xe2x80x94CH(CH3)CH(CH3)xe2x80x94, and x is a number between about 6 and about 20. Z can preferably contain a poly(oxyethylene) group. The oxyalkylene units in the poly(oxyalkylene) can be the same, such as in poly(oxypropylene), or can be present as a mixture, such as in a straight or branched chain of randomly distributed oxyethylene and oxypropylene units i.e., poly(oxyethylene-co-oxypropylene), or as in a straight or branched chain blocks of oxypropylene units. The poly(oxyalkylene) chain can be interrupted by or include one or more catenary linkages such as where Z includes a group of the formula xe2x80x94Oxe2x80x94CH2xe2x80x94CH(Oxe2x80x94)xe2x80x94CH2xe2x80x94Oxe2x80x94, provided that such linkages do not substantially alter the water-solubilizing character of the poly(oxyalkylene) chain. The Z group may be terminated with a hydroxyl, lower alkyl ether, alkaryl ether, or fluoroalkyl ether, for example, xe2x80x94OCH3, xe2x80x94OCH2CH3, xe2x80x94OC6H4C(CH3)2CH2C(CH3)2CH3, xe2x80x94OC6H4(C9H19)2, xe2x80x94OC12H25, xe2x80x94OC14H29, xe2x80x94OC16H33, or xe2x80x94O-QRf (where Q and Rf are as defined supra); and
n is a number from 1 to 6.
Among preferred examples of Formula I surfactants are
C8F17SO2N(CH3)(CH2CH2O)7CH3, C4F9SO2N(CH3)(CH2CH2O)7CH3,
C8F17SO2N(CH3)(CH2CH2O)9C8H17,
C8F17SO2N(CH3)(CH2CH2O)10C6H4C(CH3)2CH2C(CH3)2CH3, and
C8F17SO2N(CH3)(CH2CH2O)10C12H25.
Fluoroaliphatic group-containing nonionic surfactants, including those depicted in formula I, may be prepared using known methods including those methods described in U.S. Pat. No. 2,915,554 (Albrecht et al.), incorporated herein by reference. The Albrecht patent describes the preparation of fluoroaliphatic group-containing nonionic compounds from active hydrogen-containing fluorochemical intermediates, such as fluoroaliphatic alcohols (e.g., RfC2H4OH), acids (e.g., RfSO2N(R)CH2CO2H), and sulfonamides (e.g., RfSO2N(R)H), by reaction of the intermediates with, for example, ethylene oxide to yield, respectively, RfC2H4(OC2H4)nOH, RfSO2N(R)CH2CO2(C2H4O)nH, and RfSO2N(R)(C2H4O)nH, where n is a number greater than about 3 and R is a hydrogen or a lower alkyl group (e.g., from 1 to 6 carbon atoms). Analogous compounds may be prepared by treating the intermediate with propylene oxide. The fluoroaliphatic oligomers disclosed in U.S. Pat. No. 3,787,351 (Olson), and certain fluorinated alcohol-ethylene oxide condensates described in U.S. Pat. No. 2,723,999 (Cowen et al.), whose descriptions are incorporated herein by reference, are also considered useful. Fluoroaliphatic group-containing nonionic surfactants containing hydrophobic longchain hydrocarbon groups may be prepared by reacting a fluoroaliphatic epoxide with, for example, an ethoxylated alkylphenol or alcohol, such as CH3C(CH3)2CH2C(CH3)2C6H4(OC2H4)9.5OH or C12H25(OC2H4)9OH, respectively, in the presence of BF3 etherate. They may also be prepared by first converting the ethoxylated alkylphenol or alcohol to a chloride by reaction with thionyl chloride, then reacting the resulting chloride with a fluoroaliphatic sulfonamide containing an active hydrogen, for example C8F17SO2NH(CH3), in the presence of sodium carbonate and potassium iodide.
A class of useful non-fluorinated, nonionic polyoxyethylene-containing hydrophilic surfactants, that may be used alone or in conjunction with the fluoroaliphatic group-containing nonionic surfactants, may be represented generally by the following Formula II:
Rh-Z-(C2H4O)xxe2x80x94C2H4-Z-Rhxe2x80x2xe2x80x83xe2x80x83(II) 
wherein:
Rhxe2x80x2 is an alkyl or an aryl group, or a combination thereof, that may be substituted or unsubstituted and that contains from 2 to about 20 carbon atoms whose skeletal chain may be straight-chained, branched, or, if sufficiently large, cyclic, or any combination thereof, and the skeletal chain can also optionally include one or more heteroatoms such as oxygen, hexavalent sulfur, and trivalent nitrogen atoms bonded to the carbon atoms of the skeletal chain;
Rhxe2x80x2 is a hydrogen atom or is an alkyl or an aryl group as described supra for Rh;
one or both of Rh and Rhxe2x80x2 may contain a polydialkylsiloxane group of the formula, Rxe2x80x94(Si(R)2xe2x80x94O)nxe2x80x94Si(R)2xe2x80x94, where all the depicted R groups are independently selected as alkyl or aryl groups having from 2 to about 10 carbon atoms that may be substituted or unsubstituted, straight-chained or branched, cyclic or acyclic, and may contain one or more catenary heteroatoms; and wherein n can be chosen such that n is between 2 and about 40, preferably 2 and about 20, and such that the weight percent of polyoxyethylene in the surfactant is between about 20 and 80 percent, preferably between 30 and 60 percent.
Z is an oxygen or sulfur atom or is of the formula xe2x80x94COxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94CONHxe2x80x94, or xe2x80x94N(R)xe2x80x94 where R is a substituted or unsubstituted alkyl or aryl group having from 1 to 10 carbon atoms that may contain heteroatoms such as oxygen, sulfur, or nitrogen, and may contain one or more ethylene oxide groups; where R is an alkyl group, that alkyl group may be cyclic or acyclic; and
x is a number selected such that the weight percent of ethylene oxide in the surfactant is between about 20 and 80 percent, preferably from about 40 to about 70 percent.
Representative hydrocarbon surfactants according to Formula II above include ethoxylated alkylphenols (such as the Triton TX, Igepal CA and Igepal CO series, commercially available from Union Carbide Corp. and Rhone-Poulenc Corp. respectively), ethoxylated dialkylphenols (such as the Igepal DM series, also commercially available from Rhone-Poulenc Corp.), ethoxylated fatty alcohols (such as the Tergitol series, commercially available from Union Carbide Corp.) and polyoxyethylene fatty acid diesters (such as the Mapeg DO series, commercially available from PPG Industries, Inc.).
Another class of non-fluorinated, nonionic polyoxyethylene-containing surfactants useful in combination with the fluoroaliphatic surfactants in accordance with the invention may be described by the following Formula III: 
wherein:
n and m are numbers between 2 and about 20 and are chosen such that the weight percent of polyoxyethylene in the surfactant is between 20 and 80 percent, preferably between 30 and 60 percent; and
each R is selected independently from one another as an alkyl or an aryl group that may be substituted or unsubstituted and that contain from 2 to about 20 carbon atoms whose skeletal chain may be straight-chained, branched, or, if sufficiently large, cyclic, or any combination thereof; such skeletal chain can also optionally include one or more heteroatoms such as oxygen, hexavalent sulfur, and trivalent nitrogen atoms bonded to the carbon atoms of the skeletal chain.
Another class of useful non-fluorinated, nonionic polyoxyethylene-containing surfactants useful in the practice of the invention alone or in combination with the one or more fluoroaliphatic surfactants include those organosiloxane compounds that may be represented generally by the following Formula IV: 
wherein:
n, x, y, and z denote the number of repeating units in the depicted surfactant and are chosen such that the weight percent of polyethylene oxide in the surfactant is between 20 and 80 percent, preferably between 40 and 70 percent, and most preferably between 40 and 60 percent. It will be understood that the recurring siloxane units in the depicted formula may be randomly situated in the surfactant molecule;
Q is a multivalent, generally divalent, linking group, or is a covalent bond, that provides a means to link the silicon atom to the depicted oxyalkylene group; Q can comprise a heteroatom-containing group, e.g., a group containing xe2x80x94Oxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94CnH2nOxe2x80x94, or xe2x80x94OCnH2nOxe2x80x94 where n is a number from 1 to 6; and
each R is selected independently from one another as an alkyl or an aryl group that may be substituted or unsubstituted and that contain from 2 to about 20 carbon atoms whose skeletal chain may be straight-chained, branched, or, if sufficiently large, cyclic, or any combination thereof, and the skeletal chain can also optionally include one or more heteroatoms such as oxygen, hexavalent sulfur, and trivalent nitrogen atoms bonded to the carbon atoms of the skeletal chain.
Useful organosiloxane surfactants of the type depicted by Formula IV include ethoxylated polydimethylsiloxanes, such as Silwet L-77, commercially available from Union Carbide Corp.
Another class of hydrophilic surfactants useful in the invention includes monoglycerides, with preferred monoglyceride surfactants being those derived from glycerol and medium to long chain length (i.e., C8 to C16) fatty acids such as caprylic, capric, and lauric acids. See, e.g., PCT International Publication Number WO 00/71789, the entire description of which is incorporated herein by reference. Preferably, the monoglycerides can be derived from C10 to C12 fatty acids and can be foodgrade and Generally Regarded as Safe (xe2x80x9cGRASxe2x80x9d) materials. Examples of preferred monoglycerides include glycerol monolaurate, glycerol monocaprate, and glycerol monocaprylate. Because monoglycerides are typically available in the form of mixtures of unreacted glycerol, monoglycerides, diglycerides, and triglycerides, it can be preferred to use mixtures that contain a high concentration (e.g., greater than about 80 wt. %, preferably greater than about 85 wt. %, more preferably greater than about 90 wt. %, and most preferably greater than about 92 wt. %) of the monoglyceride. A convenient way to determine whether one of the aforementioned mixtures, or even a particular monoglyceride, will work in the invention, is to calculate the hydrophilic-lipophilic balance (xe2x80x9cHLB valuexe2x80x9d) for the mixture. Typically, the HLB value of one of the aforementioned mixtures decreases with increasing fatty acid chain length, and also decreases as the diglyceride and triglyceride content in the mixture increases. Useful materials (including pure monoglycerides) typically have HLB values of about 4.5 to about 9, more preferably from about 5.3 to about 8. Examples of particularly useful commercially available materials include those available from Med-Chem Laboratories, East Lansing, Mich., under the tradename LAURICIDEN(trademark), and Dimodan ML-90, a glycerol monolaurate of 90% purity, available from Danisco USA, Inc. through distributor Gillco Ingredients, Vista, Calif.
Another class of hydrophilic surfactant useful in the present invention alone or with any one or more of the monoglyceride surfactants described above are the fatty acid esters of anhydrosorbitol, such as SPAN(trademark) 20 (sorbitan monolaurate) and SPAN 40 (sorbitan monopalmitate) available from ICI Americas Inc., EXACT(trademark) 4023 available from Exxon, and Montell(trademark) DP-8340 available from Montell, and their polyoxyethylene derivatives, such as TWEEN(trademark) 20 and TWEEN 40, available from ICI Americans Inc. Fatty acid chain lengths of 8 to 16 carbons are preferred, with 12 to 16 can be preferred.
Embodiments of microfibrillated articles of the invention can be prepared by blending or otherwise uniformly mixing a hydrophilic surfactant into a solid melt-processable polymer, e.g., by intimately mixing hydrophilic surfactant with pelletized or powdered melt-processable polymer, and melt extruding the mixture into a film or web using any process for producing such films or webs, such as by conventional extruding, co-extruding, etc.
Hydrophilic surfactant can be added to a melt-processable polymer in an amount sufficient to improve hydrophilicity of the microfibrillated article, e.g. of microflakes or microfibers of the article. Enough hydrophilic surfactant should be used to produce a desired hydrophilicity, but not so much to prevent processing of the mixture of melt-processable polymer and hydrophilic surfactant to form a microfibrillated article. Hydrophilic surfactant should not be added in an amount that would cause the product of the mixture to become unduly weak or to break when melted, stretched, or oriented, or unable to be microfibrillated. Useful amounts of hydrophilic surfactant included in a melt-processable polymer can vary depending on the particular chemistries of each component, and other factors. Examples of useful amounts can be in the range from about 1 to about 10 parts by weight hydrophilic surfactant based on 100 parts by weight melt-processable polymer, with the range from about 1 to about 5 parts by weight hydrophilic surfactant, based on 100 parts by weight melt-processable polymer, being preferred.
Another type of useful hydrophilic component includes hydrophilic polymers, which can be any polymeric material that has a hydrophilic chemistry, and, according to the invention, that can be incorporated into a microfibrillated article to allow production of microflakes or microfibers having a desired hydrophilicity.
Examples of hydrophilic polymers include known polymeric materials such as carboxylic acid containing polymers, e.g. polymers and copolymers synthesized from acrylic acid and/or methacrylic acid including salts thereof, polyacrylamides, polyesters, hydroxymethylcellulose, hydroxypropylcellulose and other polymers. In certain types of hydrophilic polymers, one or more functional groups are included on the backbone of the polymer to enhance the hydrophilic nature of the polymer. For example, a hydrophilic polymer may include any type of polymeric backbone that contains in-chain hydrophilic groups, pendent hydrophilic groups, terminal hydrophilic groups, or combinations thereof. Examples of hydrophilic groups include hydroxyl groups, oxyalkylene groups, amino groups, carboxylic acid groups, amido groups, cyclic amido groups, and sulfonate groups, among others. Exemplary oxyalkylene groups may be oxyethylene or a combination of oxyethylene with oxypropylene, oxybutylene, or both. Cyclic amido groups may be 2-pyrrolidinonyl, 2-piperidinonyl, and the like. Sulfonate groups may be sulfonic acid groups and salts thereof. Carboxylate groups may be carboxylic acid groups and salts thereof. Specific examples of important hydrophilic polymers include sulfonated polyesters; polyvinylpyrrolidone; blends of polyvinylpyrrolidone with melt processable carboxylic acid containing copolymers; and polyacrylamides such as poly(dialkyl acrylamides) (e.g., poly(N,N-dimethylacrylamide). Melt processable carboxylic acid containing copolymers preferred for blends with polyvinylpyrrolidone are ionomers, for example, ionomer copolymers of ethylene and acrylic or methacrylic acid.
A hydrophilic polymer itself may or may not be xe2x80x9cmelt-processable.xe2x80x9d According to the invention, hydrophilic polymers, melt-processable or otherwise, may be added to a melt-processable polymer in an amount sufficient to improve hydrophilicity, but also sufficient to retain properties of the film that allow processing of the melt-processable polymer to form a film that is a hydrophilic microfibrillatable film.
The amount of hydrophilic polymer included in any particular microfibrillatable film or microfibrillatable article can be any amount that will result in a desirably hydrophilic microfibrillated article, including an amount that will improve the hydrophilicity of a less hydrophilic melt-processable polymer.
The particular amount of hydrophilic polymer used in any specific microfibrillated article can be based on a variety of factors such as the desired hydrophilicity; the chemistry of the hydrophilic polymer; the chemistry of the melt-processable polymer or other ingredients; processing conditions and physical properties of the ingredients, such as the ability of the mixture of hydrophilic polymer and melt-processable polymer to be extruded, oriented, microfibrillated; etc. Broadly, amounts between 1 to 70 parts by weight hydrophilic polymer per 100 parts total hydrophilic polymer and melt-processable polymer may be considered useful. Typical amounts of hydrophilic polymer versus melt-processable polymer may be in range from about 10 to 50 parts by weight hydrophilic polymer per 100 parts total hydrophilic polymer and melt-processable polymer, with the range between 20 and 30 parts by weight hydrophilic polymer being sometimes preferred. The exact amount for any hydrophilic polymer-melt-processable polymer combination will depend on many factors. As an example of one class of materials, preferred relative amounts of sulfonated polyester in a polyethylene or polypropylene may be in the range of 10 to 30 wt. %, more preferably 25 to 30 wt. % sulfonated polyester, per total polymer.
Once a microfibrillatable material is prepared from a melt-processable polymer and a hydrophilic component, the material can be microfibrillated to produce a microflake or microfiber surface by any of a variety of known and understood methods.
The term xe2x80x9cmicrofibrillation,xe2x80x9d as used herein, refers to methods of imparting energy to liberate microfibers, microflakes, or similarly sized and shaped structures from a microfibrillatable polymeric film. Some methods for doing this are known in the art of processing polymeric materials, and include methods of imparting a gaseous fluid using, for example, ultrasound techniques, and methods of imparting liquid fluids such as water, for example using high-pressure water jets. Optionally, prior to microfibrillation, a film may be subjected to other mechanical steps to produce macroscopic microfibers from the microfibrillatable material, such as by the use of a rotating drum or roller having cutting elements such as needles or teeth in contact with the moving film, or by twisting, brushing (as with a porcupine roller), rubbing, for example with leather pads, and flexing.
A microfibrillated surface is a surface that includes microflakes or microfibers from one or more layers of a microfibrillatable material. The microflakes or microfibers are portions of the microfibrillatable material that have been at least partially mechanically separated or fragmented from the continuous film. Those portions may be viewed as or considered or referred to as microfibers, microflakes, or other forms of similarly sized and shaped fragmented pieces of the film, typically having a size and shape that depends on the particular microfibrillatable material and its physical and chemical properties, such as the type and degree of orientation, the presence and size of voids, multiple layers, layer thickness, spherulites, etc. One example of such a fragmented form is microfibers, which, based on these factors, can be typically relatively flat, thin, or elongate, e.g., xe2x80x9cribbon-shaped,xe2x80x9d with a typically rectangular cross section. Other forms may be relatively larger than microfibers, and may be shaped more as a flat, rectangular xe2x80x9cflakexe2x80x9d or xe2x80x9cmicroflake.xe2x80x9d The microfibers and microflakes preferably remain attached to the microfibrillated material at one end, but may also become completely detached from the base film.
Microfibers in particular typically have a rectangular cross section with a cross sectional aspect ratio (transverse width to thickness) ranging from about 1.5:1 to about 20:1, preferably from 3:1 to 9:1. Preferred microfibers can also have one or more of the following features or dimensions: an average effective diameter of from 0.01 to 10 microns, preferably of less than 5 microns; an average cross-sectional area of 0.5xcexc2 (microns squared) to 3.0xcexc2, preferably from about 0.7xcexc2 to 2.1xcexc2. Further, the sides of the rectangular shaped microfibers are not normally smooth, but may have a scalloped appearance in cross section. Preferred microfiber surfaces may exhibit a surface area of at least 0.25 square meters per gram, as measured using an Autosorb-6 Physisorption Analyzer (Quantachrome Instruments, Boynton Beach, Fla.) using nitrogen as the absorbate.
If a voided or foamed material is biaxially oriented, after microfibrillation the majority of the material""s surface comprises schistose structures, e.g., microflakes. These structures have an average thickness of 1 to 20 micrometers, preferably less than 5 micrometers, and an average width of from one to hundreds of micrometers, preferably from about 5 to 30 micrometers. These schistose structures can typically exhibit surface areas greater than 0.5 m2/g, preferably greater than 0.7 m2/g, as measured using an Autosorb-6 Physisorption Analyzer (Quantachrome Instruments, Boynton Beach, Fla.) with nitrogen as the absorbate.
One method of microfibrillating a film surface is with fluid jets. In this process, one or more jets of a fine fluid stream impact the surface of a microfibrillatable material which may be supported by a screen or moving belt, thereby releasing microfibers or microflakes from a film""s polymer matrix. The degree of microfibrillation is dependent on the exposure time of the microfibrillatable material to the fluid jet, the pressure of the fluid jet, the cross-sectional area of the fluid jet, the fluid contact angle, the polymer properties, and to a lesser extent, the fluid temperature.
Any type of liquid or gaseous fluid may be used. Liquid fluids may include water or organic solvents such as ethanol or methanol. Suitable gases such as nitrogen, air, or carbon dioxide may be used, as well as mixtures of liquids and gases. Any such fluid is preferably non-swelling (i.e., is not absorbed by the film). The fluid can preferably be water.
The fluid temperature may be elevated, although suitable results may be obtained using ambient temperature fluids. The pressure of the fluid should be sufficient to impart some degree of microfibrillation to at least a portion of a microfibrillatable material, and suitable conditions can vary widely depending on the fluid, the nature of the polymeric material, including the composition and morphology, configuration of the fluid jet, angle of impact, and temperature. Typically, the fluid can be water at room temperature and at pressures of at least 3400 kPa (500 psi), although lower pressure and longer exposure times may be used. Such fluid will generally impart a minimum of 5 watts/cm2 or 10 W/cm2 based on calculations assuming incompressibility of the fluid, a smooth surface, and no losses due to friction.
The jets may be configured such that all or part of the film surface is microfibrillated. Alternatively, the jets may be configured so that only selected areas of the film are microfibrillated. Certain areas of the film may also be masked, using conventional masking agents, to leave selected areas free from microfibrillation. Likewise, the process may be conducted so that the microfibrillated surface penetrates only partially, or fully through the thickness of a single microfibrillatable material layer of a multi-layer microfibrillatable film, or fully or partially through one or more adjacent microfibrillatable material layers. If it is desired that the microfibrillation extend through the entire thickness of a multi-layer microfibrillatable film, conditions may be selected so that the integrity of the microfibrillated article is maintained and the film is not severed into individual yarns or microfibers.
Examples of products and processes that may be useful with those of the invention are described in Assignee""s copending U.S. patent application Ser. No. 09/974,040, entitled xe2x80x9cMicrofiber Articles from Multi-Layer Substrates,xe2x80x9d filed on Oct. 9, 2001, and Ser. No. 09/858,273, entitled xe2x80x9cMicrofiber-Entangled Products and Related Methods,xe2x80x9d filed May 15, 2001, each of which is incorporated herein by reference.
A hydroentangling machine, for example, can be used to microfibrillate a surface of a microfibrillatable material, by exposing the microfibrillatable material to fluid jets. Alternatively, a pressure water jet, with a swirling or oscillating head, may be used, which allows manual control of the impingement of the fluid jet. Such machines are commercially available.
Microfibrillation may be accomplished by other methods as well, as will be understood by the skilled artisan, e.g., by immersing a microfibrillatable material in a high energy cavitating medium, e.g., and achieving cavitation by applying ultrasonic waves to the fluid.